US20070223095A1 - Optical device, system and method - Google Patents

Abstract

Methods and systems are disclosed related to optical elements. An apparatus for making an optical device can be configured to divide an angular pattern into a plurality of sub-angular regions. Then, micro-wedge configurations can be determined for directing light to the sub-angular regions. Subsequently, an array of micro-wedges can be generated according to the micro-wedge configurations, such that adjacent micro-wedges in the array have different configurations.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims priority under 35 U.S.C. § 120 on and is a Continuation of U.S. patent application Ser. No. 09/507,466 entitled “OPTICAL DEVICE, SYSTEM AND METHOD” filed on Feb. 22, 2000, which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
• The present invention relates generally to optics and optical systems and devices. The present invention also relates to a device for forming an homogenized light pattern. The present invention also relates to a method of making an optical device.
BACKGROUND OF THE INVENTION
• Known techniques for homogenizing light make use of arrayed micro-lenses, diffractive diffusers, ground glass diffusers, and holographically-generated diffusers. Micro-lens arrays homogenize light by creating an array of overlapping diverging cones of light. Each cone originates from a respective micro-lens and diverges beyond the focal spot of the lens. In the known arrays, the individual lenses are identical to each other. Ground glass diffusers are formed by grinding glass with an abrasive material to generate a light-scattering structure in the glass surface.
• Micro-lens arrays, ground glass diffusers and holographic diffusers all have the disadvantage of not being able to control the angular spread of the homogenized, diverging light. Light in general has an angular spread that is fairly uniform over a desired angular region, but the boundaries of the angular region are blurred. With the known diffuser methods, the energy roll-off at the edge of the desired angular spread can extend well beyond this region.
• Diffractive diffusers can be used to control the angular spread of the output light, but such diffusers are limited with respect to the amount of spread that they can impart to the output light. Due to fabrication limitations for short wavelength sources, visible or below, and limitations in the physics of the structures for longer wavelengths the maximum angular spread is limited. Further, diffractive diffusers used in their traditional binary form can include a significant amount of background energy and the patterns must be symmetric about the optical axis.
• Thus, there is a need for a device which can homogenize light while controlling a broad angular spread of the homogenized, diverging light beam. Additionally, there is a need for a method of making an improved device for homogenizing light.
SUMMARY OF THE INVENTION
• The disadvantages of the prior art are overcome to a great extent by the present invention. The present invention relates to an optical device formed of a plurality of optical elements. The elements may be used to direct portions of an incident light beam in predetermined, respective directions. The optical elements may be formed adjacent to each other in a two-dimensional array. Adjacent elements may have different shapes. The locations of the elements in the array may be essentially random with respect to the directions of the corresponding light beam portions.
• According to preferred embodiments of the invention, the optical elements may be formed of transparent or reflective materials. The output surfaces of the respective elements may be flat and planar or they may be curved and non-planar.
• According to another aspect of the invention, the optical device may be used to form an angular pattern. Alternatively, the device may be used to split the incoming beam into sub-beams.
• The present invention also relates to an optical system that has a light source and an optical homogenizing device. The optical device may be formed of a large number of micro-wedges. The wedges may be used to form respective non-adjacent portions of a desired angular pattern. In a preferred embodiment of the invention, adjacent wedges may be formed with different three-dimensional conjurations.
• The present invention also relates to a method of making a multi-faceted optical device. The method includes the steps of (1) dividing an angular pattern into sub-angular regions, (2) determining micro-wedge configurations for directing beam portions to the sub-angular regions, and (3) generating an array of micro-wedges, according to the determined configurations, such that adjacent wedges have different configurations.
• According to another aspect of the invention, the two-dimensional arrangement or ordering of the wedges in the device-array is essentially random with respect to the two-dimensional arrangement of the sub-angular regions in the pattern. According to this aspect of the invention, the respective micro-wedge configurations may be assigned to random locations in the array. Thus, the relative positions or order of the wedges in the array has essentially no relationship to the relative positions or order of the sub-angular regions in the pattern. According to yet another aspect of the invention, the output surface slopes for the micro-wedges are calculated by a programmed general-purpose computer based on the locations of the respective sub-angular regions in the desired pattern.
• In a preferred embodiment of the invention, appropriate phase tare surfaces may be used to divide the output surfaces of the micro-wedges into stepped or terraced surfaces, to thereby reduce the overall thickness of the optical device.
• According to yet another aspect of the invention, an optical homogenizing device is formed of a tiled array of sub-devices, where each sub-device has randomly arranged micro-wedges. The tiled device may be used, for example, to handle large diameter input beams.
• Thus, the present invention provides a method and apparatus for homogenizing a beam of light. The invention makes use of micro-structures in an array where each optical element or micro-wedge is different from its adjacent neighbor in size and slope. The array of different micro-wedges can homogenize light sources without the disadvantages of the prior art. Various combinations and alterations to the micro-wedge array may include: adding a phase bias to the micro-wedges to further scramble the incoming beam; and adding a lens function to the surface of the array or to the back surface of the device.
• The present invention may be used to homogenize light sources, perform beam splitting operations, and/or to redirect light in a given direction.
• These and other advantages and features of the invention will become apparent from the following detailed description of the invention which is provided in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic perspective view of an optical system constructed in accordance with a preferred embodiment of the invention.
• FIG. 2 is a partial plan view of the optical device shownFIG. 1.
• FIG. 3 is a cross sectional view of the optical device ofFIG. 2, taken along the line3-3.
• FIG. 4 illustrates a method of making the optical device ofFIGS. 2 and 3.
• FIG. 5 is a perspective view of another optical device constructed in accordance with the present invention.
• FIG. 6 is a partial cross sectional view of yet another optical device constructed in accordance with the present invention.
• FIG. 7 is a partial cross sectional view of yet another optical device constructed in accordance with the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• Referring now to the drawings, where like reference numerals designate like elements, there is shown inFIG. 1 anoptical system10 constructed in accordance with a preferred embodiment of the invention. Theoptical system10 has alight source12 for generating alight beam14, and anoptical device16 for homogenizing thebeam14. In operation, thedevice16 may be used to form anangular pattern18. In the illustrated embodiment, the pattern constitutes the letter “H.” In alternative embodiments, thedevice16 may be used to form a wide variety of patterns, including for example a split beam pattern.
• In a preferred embodiment of the invention, theoptical device16 is formed of an array ofoptical wedges22,24. Thewedges22,24 receive incident portions of theinput beam14 and direct thebeam portions46,48 towardrespective portions50,52 of theangular pattern18.
• As shown in more detail inFIG. 2, theoptical device16 may be formed of numerous square or rectangular-shaped micro-wedges22,24,26,28,30,32,34,36,38,40,42,44. Although only twelvewedges22,24,26,28,30,32,34,36,38,40,42,44 are shown inFIG. 2, theoptical device16 may have ten thousand ormore wedges22,24,26,28,30,32,34,36,38,40,42,44 distributed randomly across its output surface. The configuration (i.e., three-dimensional shape) and slope of eachwedge22,24,26,28,30,32,34,36,38,40,42,44 may be different than the configuration and slope of eachadjacent wedge22,24,26,28,30,32,34,36,38,40,42,44. In a preferred embodiment of the invention, thewedges22,24,26,28,30,32,34,36,38,40,42,44 have flat, planar optical output surfaces (FIG. 3). The present invention should not be limited, however, to the preferred embodiments shown and described herein in detail.
• In a preferred embodiment of the invention, the areas ofadjacent wedges22,24,26,28,30,32,34,36,38,40,42,44 are made unequal by selecting the lengths of theedges142 appropriately. As shown inFIG. 2, for example, the lengths L1 and L2 of edges (or boundaries)142 extending in a first direction may be made not equal to each other (L1≠L12). Similarly, the lengths L3 and L4 ofedges142 that extend in the orthogonal direction may be made not equal to each other (L3≠L4). By constructing thewedges22,24,26,28,30,32,34,36,38,40,42,44 in different sizes by making theirside edges142 of different lengths, interference effects may be reduced.
• Thearrows60 inFIG. 2 represent the direction of increasing thickness for therespective wedges22,24,26,28,30,32,34,36,38,40,42,44 (where thickness is measured in a direction perpendicular to the plane of the page). Thus, thefirst wedge22 increases in thickness from left to right inFIG. 2, whereas thesecond wedge24 increases in thickness from top to bottom as viewed inFIG. 2. Athird wedge26 increases in thickness in a direction toward the lower left corner ofFIG. 2. Afourth wedge32 increases in thickness in a direction toward the upper left corner ofFIG. 2.
• Phase tare surfaces70,72,74,76,78,80,82,84 may be provided to reduce the overall thickness of theoptical device16. Thus, thefirst wedge22 is separated by atare surface70 into first andsecond portions90,92. The slopes (60) of the first andsecond portions90,92 may be equal to each other. That is, the planar output surfaces of the first andsecond portions90,92 may be parallel to each other. Likewise, thesecond wedge24 is separated by atare surface72 into first and secondparallel portions94,96. The slopes (designated by arrows60) of the twoportion94,96 may be equal to each other.
• The tare surfaces70,72,74,76,78,80,82,84 in effect operate to fold the output surfaces of the micro-wedges22,24,26,28,30,32,34,36,38,40,42,44. The tare surfaces70,72,74,76,78,80,82,84 may be especially useful when the slopes (60) of the wedge output surfaces are relatively great. The heights of the tare surfaces70,72,74,76,78,80,82,84 (measured in the direction from top to bottom as viewed inFIG. 3) may be a function of the wavelength of the incident light, if desired. For example, the heights of the tare surfaces70,72,74,76,78,80,82,84 may be integer multiples of the wavelength of theincoming light beam14.
• As shown inFIG. 3, the phase tare surfaces70,72,74,76,78,80,82,84 may lie in planes that are essentially parallel to the propagation direction of theinput beam14. InFIG. 3, the surfaces of the micro-wedges located behind the cross sectional line3-3 are not shown for the sake of clarity of illustration. In other words,FIG. 3 represents only a thin slice of theoptical device16 taken along the line3-3.
• In operation, thelight source12 transmits theinput beam14 toward theoptical device16. Theinput beam14 may have an uneven intensity distribution across its cross section. Thebeam14 is directed onto theoptical device16 such that portions of thebeam14 are incident onrespective wedges22,24,26,28,30,32,34,36,38,40,42,44. Thewedges22,24,26,28,30,32,34,36,38,40,42,44 direct thebeam portions46,48 in predetermined directions to form an homogenizedangular pattern18. Thehomogenized pattern18 may have a substantially uniform light intensity distribution. Thebeam portions46,48 are transmitted in different directions since eachwedge22,24,26,28,30,32,34,36,38,40,42,44 is different from its adjacent and neighboringwedges22,24,26,28,30,32,34,36,38,40,42,44 in size and/or slope (60). Thus, thelight output46,48 of eachwedge22,24,26,28,30,32,34,36,38,40,42,44 is directed or angled toward a particularsub-angular region50,52 of the desiredangular spread18. Although the angular spread orpattern18 is shown as the letter “H” inFIG. 1, theoptical device16 also may be used to split theinput light beam14 and/or to form a variety of other patterns.
• Referring now toFIG. 4, a preferred method of making theoptical device16 includes the step of dividing the desiredpattern18 into small sub-angular regions (Step150). The size of theincident beam14 may be used to determine an appropriate number of sub-angular regions into which thepattern18 should be divided. If the cross sectional area of thebeam14 is relatively large, then a relatively large number of sub-angular regions may be employed. If the cross,sectional area of thebeam14 is relatively small, then a relatively small number of sub-angular regions may be employed. Although only twosub-angular regions50,52 are shown inFIG. 1 for the sake of clarity, the present invention may be practiced by dividing theentire pattern18 in to ten thousand or more such sub-angular regions. The number of sub-angular regions may be related to the number of wedges to be formed in theoptical device16.
• Then, using appropriate geometric calculations, a slope and a three dimensional configuration for each wedge is determined such that the wedge will direct a portion of the input beam to a respective sub-angular region (Step152). Then, a location within thedevice16 is randomly chosen for each calculated wedge configuration (Step154). The random placement of thewedges22,24,26,28,30,32,34,36,38,40,42,44 in theoptical device16 causes thepattern18 to have a uniform intensity. In other words, the random location of thewedges22,24,26,28,30,32,34,36,38,40,42,44 causes theinput beam14 to be homogenized.
• The output surfaces of thewedges22,24,26,28,30,32,34,36,38,40,42,44 may then be formed in a suitable substrate (e.g., glass) by gray scale photolithography, a suitable direct write method (e.g., electron beam or laser), or by another suitable technique (Step156).
• If the number of sub-angular regions in thepattern18 is less than the number of micro-wedges desired to be arrayed in thedevice16, then some of the wedges may have the same slope and size. The similar wedges will direct light energy to the same location or sub-angular region. However, the wedges with similar slopes, sizes and shapes are preferably not located adjacent one another.
• The illustratedoptical device16 may be used to increase the amount of angular spread in thepattern18 while maintaining a well defined pattern boundary158 (FIG. 1). For example, at a wavelength of two hundred forty eight, nanometers, with efficiencies of from eighty five percent to ninety five percent, depending on the shape of theoutput pattern18, a half angle of approximately seven degrees is obtainable.
• In addition, thedevice16 may be used efficiently over a broad wavelength band, including but not limited to white light. This is an advantage over diffractive diffusers since diffractive diffusers are tuned to a particular wavelength and have decreased efficiency at different wavelengths.
• According to another embodiment of the invention, an optical device100 (FIG. 5) may be formed of a tiled array ofsmaller devices16. Thetiled device100 may be used, for example, to handle large diameter input beams. The size of eachtile16 may be slightly different from the neighboringtiles16 to eliminate interference effects that might otherwise be caused by a repeating pattern. The intensity of light transmitted through eachtile16 may be different, which may cause a slight change in the amount of energy imparted to each sub-angular region in thepattern18. This effect is reduced, however, by the random placement of wedges within eachtile16.
• For certain desired angular regions, the number of sub-angular regions required to fill the region can be very large (for example, greater than ten thousand) which requires a very large number of micro-wedges. In these instances, theinput beam14 should have a small diameter to illuminate all portions of thetiles16. By decreasing the size of the individual micro-wedges, the input beam size can be reduced. The size of thewedges22,24,26,28,30,32,34,36,38,40,42,44 preferably should not be so small, however, as to cause the diffraction angle defined by the wedge apertures to become too great.
• As shown inFIG. 6, the output surfaces130 of anoptical device16′ may have slight curvatures. Thesurfaces130 may be spherical, parabolic or the like. The output surfaces130 may be separated by tare surfaces, anddiscontinuities132 similar to the tare surfaces and rectangular facet boundaries shown inFIGS. 2 and 3. The slight curvatures shown inFIG. 6 produce narrow bands of angles instead of single angles. The illustrated curvatures can help to improve the filling of largeangular patterns18 with fewer facets in theoptical device16′. The embodiment shown inFIG. 6 otherwise operates similarly to the embodiment shown inFIGS. 1-3.
• FIG. 7 displays anoptical device16″ employed in a reflection mode. In this embodiment, theinput light14 is propagated into amicro-wedge array16″. Amirror coating122 is used on the array output surfaces which reflects theinput light14 to directbeam portions46′,48′toward the respective portions of the desiredpattern18.
• The present invention may also be employed with a phase bias device or an optical lens140 as shown schematically inFIG. 1. The lens140 may be separate from theoptical device16 or it may be constructed as an integral part of theoptical device16. The lens140 may be on either side of the micro-wedges22,24,26,28,30,32,34,36,38,40,42,44. The lens140 may be used, for example, to perform an optical Fourier-transform operation.
• According to yet another aspect of the invention, the facet boundaries142 (FIG. 2) of each micro-wedge22,24,26,28,30,32,34,36,38,40,42,44 may be randomized to further reduce the effects of discontinuities at theboundaries142.
• Reference has been made to preferred embodiments in describing the invention. However, additions, deletions, substitutions, or other modifications which would fall within the scope of the invention defined in the claims may be implemented by those skilled in the art without departing from the spirit or scope of the invention. Accordingly, the invention is not to be considered as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims (17)

1. An apparatus for making an optical device comprising:

means for dividing an angular pattern into a plurality of sub-angular regions;

means for determining micro-wedge configurations for directing light to said sub-angular regions; and

means for subsequently, generating an array of micro-wedges according to said micro-wedge configurations, such that adjacent micro-wedges in said array have different configurations.

2. The apparatus ofclaim 1, wherein the two-dimensional arrangement of said micro-wedges in said array is essentially random with respect to the two-dimensional arrangement of said sub-angular regions of said pattern.

3. The apparatus ofclaim 2, further comprising

means for assigning said micro-wedge configurations to random locations in said array.

4. The apparatus ofclaim 3, wherein means for determining micro-wedge configurations includes means for calculating output surface slopes for said micro-wedges.

5. The apparatus ofclaim 1, wherein said means for generating said array a means for forming phase tare surfaces in said micro-wedges.

6. The apparatus ofclaim 1, wherein said means for generating includes means for forming output surfaces for said micro-wedges.

7. The apparatus ofclaim 1, further comprising:

means for providing a plurality of tiles of said micro-wedge arrays.

8. An optical device, comprising:

a substrate, the substrate adjacent to a medium, the substrate comprising:

a smooth regularly shaped exterior surface; and

an irregularly shaped exterior output surface, said irregularly shaped exterior output surface comprising:

a first optical element for directing a first portion of an incident light beam exiting the irregularly shaped exterior output surface via the first optical element in a predetermined first direction; and

a second optical element, adjacent to said first optical element on the irregularly shaped exterior surface and formed on a same side of said irregularly shaped exterior output surface as said first optical element, for directing a second portion of said incident light beam exiting the irregularly shaped exterior output surface via the second optical element in a predetermined second direction in the medium different from said predetermined first direction in the medium, the light beam exiting in the first and second directions contributing to a portion of a predetermined pattern;

wherein said first optical element is of a first shape, said second optical element is of a second shape different from said first shape, said first and second shapes are microwedges, and said first optical element and said second optical element have non-textured and substantially planar output surfaces.

9. The device ofclaim 8, wherein said first and second optical elements are transparent.

10. The device ofclaim 8, wherein said first and second optical elements are reflective.

11. The device ofclaim 8, further comprising a lens for performing a Fourier transform operation.

12. The device ofclaim 8, further comprising a device for optically modifying said incident light beam.

13. The device ofclaim 8, wherein said optical elements are arranged to split the incident light beam.

14. An optical device, comprising:

a substrate comprising:

a first smoothly regular surface; and

a second surface, wherein the second surface has at least two portions, a first portion and a second portion, the first portion has a first portion surface and the second portion has a second portion surface, the first and second portion surfaces being adjacent and non-continuous, the first portion for directing a first light beam exiting the first portion in a predetermined first direction, and the second portion for directing a second light beam exiting the second portion in a predetermined second direction, the first light beam and second light beam contributing to a portion of a predetermined pattern.

15. The device ofclaim 14, wherein the first smoothly regular surface is flat.

16. The device ofclaim 14, wherein the first portion surface is curved.

17. The device ofclaim 14, wherein the first portion surface is parabolic.

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